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<a name="the_type_traits_introspection_library.tti_reason"></a><a class="link" href="tti_reason.html" title="Why the TTI Library ?">Why the
    TTI Library ?</a>
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<p>
      In the Boost Type Traits library there is compile time functionality for querying
      information about a C++ type. This information is very useful during template
      metaprogramming and forms the basis, along with the constructs of the Boost
      MPL library, and some other compile time libraries, for much of the template
      metaprogramming in Boost.
    </p>
<p>
      One area which is mostly missing in the Type Traits library is the ability
      to determine what C++ inner elements are part of a user-defined type, where
      the inner element may be a general nested type, a specific nested type such
      as a class/struct, enumeration, or a union, a function or data member, static
      function or static data member, or class template.
    </p>
<p>
      There has been some of this functionality in Boost, both in already existing
      libraries and in libraries on which others have worked but which were never
      submitted for acceptance into Boost. An example with an existing Boost library
      is Boost MPL, where there is functionality, in the form of macros and metafunctions,
      to determine whether an enclosing type has a particular nested type or nested
      class template. An example with a library which was never submitted to Boost
      is the Concept Traits Library from which much of the functionality of this
      library, related to type traits, was taken and expanded.
    </p>
<p>
      It may also be possible that some other Boost libraries, highly dependent on
      advanced template metaprogramming techniques, also have internal functionality
      to introspect a type's elements at compile time. But to the best of my knowledge
      this sort of functionality has never been incorporated in a single Boost library.
      This library is an attempt to do so, and to bring a recognizable set of interfaces
      to compile-time type introspection to Boost so that other metaprogramming libraries
      can use them for their own needs.
    </p>
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